Polyolefins are frequently the material of choice for a variety of thermoplastic parts because of their relatively low cost and superior physical properties. Polyolefins are desirable materials for many automobile interior parts for the same reasons plus the fact that polyolefins have excellent resistance to solvents and moisture. However, in contrast to their superior physical properties, polyolefins are very difficult materials to bond to which limited their usage. The causes for the difficult bonding property are low surface tension and chemical inertness of the polyolefins.
In automobile interior applications, many of the luxury versions of interior trim parts are cloth covered for improved appearance. The technology for bonding polyolefins such as polypropylene with a solvent-based primer followed by a solvent-based adhesive is widely known. It would have been an easy task to find a workable solvent-based adhesive system for the bonding of polypropylene parts. In cases where the polyolefin surface is first treated by methods like corona or gas plasma treatment, the use of a solvent-based primer may not be necessary.
The use of solvent-based adhesives and solvent-based primers in a factory environment has been disfavored in recent years. In order to meet the stringent solvent emissions requirements set up by the Environmental Protection Agency, a variety of manufacturing operations which utilizes solvent based adhesives must be changed over to water-based adhesives. Many new manufacturing operations must also be designed with water-based adhesive systems such that the use of solvents can be completely eliminated.
Replacing a solvent-based adhesive with a water based adhesive in bonding a polyolefin such as polypropylene is a very difficult task. This is because water is a polar solvent and polypropylene is a nonpolar material. When water is used as the solvent for an adhesive composition, surface treatment on the substrate is necessary in order to lower the surface tension to allow water to adequately wet the surface.
It is therefore an object of the present invention to provide a water-based adhesive composition for bonding to a polyolefin surface.
It is yet another object of the present invention to provide a water-based adhesive composition for bonding to a polyolefin surface which forms a bond of high strength and high temperature resistance.
It is a further object of the present invention to provide a water based adhesive composition for bonding to a polyolefin surface which forms a bond that is moisture-resistant.